CHARGE CURRENT SELECTION

The LP3945 and LP3946 are designed to provide a charge

current ranging from 500 mA to 950 mA, in 50 mA resolution,

to support batteries with different capacity ratings. No exter-

nal resistor is required to set the charge current in the

LP3945 and LP3946. This entirely eliminates design time,

external component board space and stability issue.

The LP3945 uses the I

current while the LP3946 has a pre-programmed charge

current.

BATTERY VOLTAGE SELECTION

The battery voltage regulation is set to 4.1V during the

manufacturing. The 4.2V option can be selected on LP3945

via the I

The Ni-MH charge mode is only available in LP3945.

END OF CHARGE (EOC) CURRENT SELECTION

The EOC thresholds can be programmed to 0.1C, 0.15C and

0.2C in the LP3945. The default value is 0.1C, which pro-

vides the highest energy storage, but at the expense of

longer charging time. On the other hand, 0.2C takes the

least amount of charging time, but yields the least energy

storage. The LP3946 has 0.1C as pre-programmed EOC

threshold. 0.15C and 0.2C options are available upon re-

quest.

No EOC function is available during Ni-MH charge cycle.

User must provide a reliable method for charge termination.

CHARGE CURRENT SENSE DIFFERENTIAL AMPLIFIER

The charge current is monitored across the internal 120 m

Ω

current sense resistor. The differential amplifier provides the

analog representation of the charge current. Charge current

can be calculated using the following equation:

Where voltage at Diff Amp output (V

charge current (I

Monitoring the Diff Amp output during constant voltage cycle

can provide an accurate indication of the battery charge

status and the time remaining to EOC. This feature is par-

ticularly useful during Ni-MH charge cycle. The current

sense circuit is operational in the LDO mode as well. It can

be used to monitor the system current consumption during

testing.

LED CHARGE STATUS INDICATORS

The LP3945 and LP3946 are equipped with two open drain

outputs to drive a green LED and a red LED. These two

LEDs work together in combinations to indicate charge sta-

tus or fault conditions. Table 2 shows all the conditions.

TABLE 2. LED Indicator Summary

Charger Status

RED

LED

GREEN

LED

Charger Off

OFF

OFF

Charging Li Ion Battery*

ON

OFF

Maintenance Mode

OFF

ON

Charging Li Ion Battery after

Passing Maintenance Mode

OFF

ON

Charging Ni-MH in Constant

Voltage Mode

ON

OFF

EN Pin = LOW

OFF

ON

LDO Mode

OFF

OFF

5.6 Hr Safety Timer Flag

ON

ON

20066514

FIGURE 4. Charge Current Monitoring Circuit (Diff-Amp)

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